1. Field of the Invention
The present invention relates to chemical mechanical polishing of wafers, and more particularly to a slurry dispenser and rinse arm and methods of performing chemical mechanical polishing.
2. Background of the Art
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semi-conductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the uppermost surface of the substrate, i.e., the exposed surface of the substrate, may become non-planar across its surface and require planarization. This occurs when the thickness of the layers formed on the substrate varies across the substrate surface as a result of the nonuniform geometry of the circuits formed thereon. In applications having multiple patterned underlying layers, the height difference between the peaks and valleys becomes even more severe, and can approach several microns.
Chemical mechanical polishing (CMP) is one accepted method of planarization. In a typical CMP system as shown in FIG. 1, a substrate 12 is placed face down on a polishing pad 14 located on a large rotatable platen 16. A carrier 18 holds the substrate and applies pressure to the back of the substrate to hold the substrate against the polishing pad during polishing. A retaining ring 20 is typically disposed around the outer perimeter of the substrate to prevent the substrate from slipping laterally during polishing. A slurry is delivered to the center of the polishing pad to chemically passivate or oxidize the film being polished and abrasively remove or polish off the surface of the film. A reactive agent in the slurry reacts with the film on the surface of the substrate to facilitate polishing. The interaction of the polishing pad, the abrasive particles, and the reactive agent with the surface of the substrate results in controlled polishing of the desired film.
One problem encountered in CMP is that the slurry delivered to the polishing pad may coagulate and along with the material being removed from the substrate may clog the grooves or other features on the pad thereby reducing the effectiveness of the subsequent polishing steps and increasing the likelihood of poor defect performance. Accordingly, rinse arms have been incorporated in some CMP systems to deliver de-ionized water or other rinse agents to the pad to facilitate rinsing of the pad of coagulated slurry and other material in the grooves and on the surface of the pad. One rinse arm, disclosed in U.S. Pat. No. 5,578,529, includes a rinse arm with spray nozzles positioned along its length to deliver a rinse agent at a pressure slightly higher than ambient to the surface of the pad. Another rinse assembly, provided by Applied Materials, Inc., Santa Clara, Calif., combines a rinse line and one or more slurry delivery lines in a single fluid delivery arm which delivers the rinse agent and/or the slurry to the center of the pad. This assembly is described in co-pending U.S. patent application Ser. No. 08/549,336, entitled "Continuous Processing System for Chemical Mechanical Polishing."
However, each of these rinse assemblies has several drawbacks. First, the rinse arm disclosed in the noted patent is prone to splashing which may transfer particles or other unwanted debris from one polishing pad to an adjacent polishing pad. In addition, the rinse arm is fixed in its position over the pad so that the pad cannot be easily removed. Still further, the rinse arm must be disposed over the center of the pad in order to deliver the rinse agent to that portion of the pad. Depending on the location of the substrate carrier relative to the pad, rinsing of the central portion of the pad may not be accomplished unless the substrate carrier is moved from the pad and polishing steps are discontinued.
The rinse assembly described in U.S. patent application Ser. No. 08/549,336 is limited in that the rinse agent is not delivered with force to the pad along the length of the rinse aim. In addition, the rinse agent is delivered at the center of the pad or where ever the dispensing end of the delivery channel is positioned.
Therefore, there exists a need to provide a rinse and slurry delivery system which is moveable from a position over the polishing pad, which does not cause uncontrolled splashing of the rinse agent, and which delivers the rinse agent over the entire surface of the polishing pad without having to be located over the entire pad.